No abstract

No abstract

No abstract

Although adult Rumex obtusifolius are problematic weeds, their seedlings are poor competitors against Lolium perenne, particularly in established swards. We investigated the possibility of using this weakness to augment control of R. obtusifolius seedlings with combinations of Gastrophysa viridula (Coleoptera: Chrysomelidae) and the rust fungus Uromyces rumicis. Rumex obtusifolius seedlings were grown in competition with L. perenne sown at different rates and times after R. obtusifolius: they competed successfully with L. perenne when sown 21 days before the grass. Sowing both species at the same time resulted in a dominant grass sward, with R. obtusifolius becoming dominant when sown 42 days prior to L. perenne. Grass sowing rate had no effect on R. obtusifolius growth or biomass. A second experiment investigated how competition from L. perenne sown 21 days after R. obtusifolius combined with damage from G. viridula and/or U. rumicis (applied at either the 3-4-or 10-13-leaf stage, or at both stages) affected the growth and final biomass of R. obtusifolius. Beetle grazing at the latter leaf stage was the only treatment that reduced R. obtusifolius biomass, although rust infection at the earlier application led to an increase in shoot and root weight. The results are discussed in terms of the potential for use of these agents in the field.

The chlorophyll content (or SPAD meter) is a simple, portable diagnostic tool that measures the greenness or relative chlorophyll content of leaves. Compared with the traditional destructive methods of chlorophyll extraction, the use of this equipment saves time, space, and resources. The objective of this study was to establish a correlation between the leaf photosynthetic pigment content (chlorophylls, carotenoids) extracted in aqueous acetone, total leaf nitrogen (N) content, and chlorophyll fluorescence Fv/Fm values with the SPAD-502 readings in sycamore (Acer pseudoplatanus), beech (Fagus sylvatica), and English oak (Quercus robur) leaves displaying visual symptoms of N deficiency. In addition, this study aimed to determine a critical foliar N content below which a reduction in photosynthetic efficiency occurs. Irrespective of species, high correlations were recorded between SPAD readings, total leaf chlorophyll and carotenoid content, foliar N content, and leaf photosynthetic efficiency as measured by chlorophyll fluorescence Fv/Fm values; however, a poor correlation between SPAD values and total chlorophyll:carotenoid ratios was obtained. In the case of Acer pseudoplatanus, Fagus sylvatica, and Quercus robur, SPAD readings lower than 25 indicated impairment of leaf photosynthetic process that in turn were correlated with a foliar N content less than 1.5%, a value associated with a critical N deficiency. Results of this study indicate that the chlorophyll content SPAD-502 m potentially offers a useful nondestructive, handheld system to aid in the evaluation of tree health. However, users should be aware of the limitations of this system. Consistency in sample collection and seasonal timing may necessitate species and cultivar calibration equations to correlate SPAD values with reductions in tree vitality.

The effects of four commercially available film-forming polymers (Bond, Designer, Spray Gard, Nu-Film-P) on disease severity of powdery mildew (Microsphaera alphitoides Griffon and Maubl.) on English oak (Quercus robur L.) and Guignardia leaf blotch (Guignardia aesculi (Peck) Stewart) on horsechestnut (Aesculus hippocastanum L.) were examined in a field experiment. In addition, a comparative evaluation of the fungicide penconazole, commercially used for powdery mildew control, was conducted. Effects on tree vitality were also assessed by measuring leaf chlorophyll fluorescence and chlorophyll concentrations. Irrespective of tree species, Nu-Film-P and Spray Gard did not significantly influence disease severity of powdery mildew and Guignardia leaf blotch. Likewise, no significant effects of these two film-forming polymers on chlorophyll fluorescence and chlorophyll content were recorded. Reduction in disease severity following spray applications of the film-forming polymers Bond and Designer was statistically comparable with penconazole. None of the film-forming polymers and fungicide evaluated was phytotoxic to the test trees. Results suggest that application of an appropriate film-forming polymer may provide a useful addition to existing methods of plant disease control.

No abstract

No abstract